As discussed in Schnell, et al., U.S. Pat. No. 6,319,465 and elsewhere, hemodialysis and other forms of extracorporeal blood treatment require the removal of blood from a patient by means of an arterial tube set, the passing of the blood to a blood processing device such as a dialyzer, and the subsequent returning of the blood to the patient again through a venous tube set.
Maintenance of good blood set access is a major cost and problem of dialysis, which is the most common extracorporeal blood treatment, although other types of blood treatment are also known, for example, passing of the blood through an absorption bed for removal of toxins or the like, hemoperfusion, and other forms of blood treatment.
Beyond the initial cost of the surgical procedure to establish a fistula or graft in the patient, the keeping of adequate blood flow in an arterialized vein or synthetic arteriovenous graft of the patient frequently involves secondary surgical intervention for reconstruction of an old blood vessel site on the patient. Alternatively, it may be necessary to establish an entirely new fistula or graft at a new site if the old one fails.
Such failure is evidenced typically by stenosis of the blood vessel, or blockage of an implanted catheter or other venous access site, with a consequent reduction in blood flow that eventually shuts down the site. Clotting is also a major cause of reduced blood flow.
If site failure is detected early enough, a less invasive technique such as balloon angioplasty can be employed to open the stenosis at a greatly reduced cost. Early detection of stenosis can be measured by a change in pressure in the blood vessel or implant that reflects a restriction beginning to form. The technique described in Omachi, U.S. Pat. No. 5,454,374, has been used to measure the baseline pressure access site for early detection of such a pressure change. Another method used by clinicians is to measure recirculation in the vessel during dialysis. As the flow is restricted in the access, the blood pumping rate indicated on the dialysis machine may exceed the flow rate of fresh blood coming into the vessel, so that some is recirculated from the venous access site to the arterial access site in the patient. This leads to inadequate dialysis since already cleansed blood is thus being reprocessed.
Various methods for measuring the degree of this recirculation are known. A method described by Krivitski determines blood flow in the access as a marker for stenosis. In this method, blood set flow and recirculation are compared between arterial and venous flow in the normal orientation, and then with reversed flow between the arterial and venous access sites, which are typically fistula needles which enter the vein. In the prior art, clinicians typically accomplished this by stopping the flow of blood, clamping all the lines, disconnecting the set or sets from the fistula needles, and then reconnecting the arterial line to the venous fistula while connecting the venous line to the arterial fistula. This of course is inconvenient and undesirable in that blood spillage and infection becomes a possibility. Accordingly, various other solutions relating to obtaining a reverse flow of blood in an extracorporeal blood circuit have been proposed, for example, Schnell, et al., U.S. Pat. Nos. 6,177,049 and 6,319,465, Krivitski, U.S. Pat. No. 6,308,737, Prosl, et al., U.S. Pat. No. 5,894,011 and Schneditz U.S. Pat. No. 5,830,365.
Also, regarding permanently implanted catheters, which are typically connected to larger veins or even the vena cava, it is known that catheter blockage may be relieved by reversing flow through the catheter and thus extending its useful life.
Accordingly, there are several reasons for why it is desirable to have an easily controlled flow reversal system in extracorporeal blood treatment.
By this invention, a flow reversal system is provided, free of slidably moving parts, and simply comprising connected flexible tubing, which has long been used in blood handling. The flow reversal system of this invention is quite inexpensive and easy to manufacture, utilizing generally conventional components, which have had long use, testing, and reliability, to obtain with ease the desired flow reversal when it is needed, with a minimal increase in the blood volume of the system because of the presence of the flow reversal apparatus, and generally free of stagnant flow areas.
By this invention, a tubular set portion is provided for circulating blood between a patient and an extracorporeal blood treatment device. This tubular set portion may be an integral part of joined arterial and venous blood flow sets, and/or fistula sets, which may otherwise be generally conventional in nature, apart from the improvement of this invention. Alternatively, the tubular set portion may be a separate set portion, which may be connected to any kind of conventional arterial and venous blood flow sets, and/or fistula sets and also connected to fistula needles, or percutaneous catheters to provide a complete flow circuit between the patient and an extracorporeal blood treatment device such as a dialyzer.
By this invention, the set portion comprises: an arterial tube for conveying blood from a patient toward the blood treatment device; a venous tube for conveying blood from the blood treatment device back toward the patient; and a pair of spaced, transverse tubes that each connect between the arterial tube and the venous tube. Each of the transverse tubes are capable of being sealed by a clamp (for clamp sealing by the usual collapse of a tube). Furthermore, the arterial and venous tubes are clamp sealable at a position between the spaced, transverse tubes.
Preferably, the wall-to-wall spacing between the transverse tubes is substantially equal to the wall-to-wall spacing of the arterial and venous tubes at a position between the transverse tubes. Furthermore, it is preferred for this wall-to-wall spacing, especially between the transverse tubes, to be so that both of the transverse tubes may be substantially completely sealed by the closure of one or two hemostat clamps or the like of a width to provide minimal residual blood volume left in the transverse tube. This is desirable since a significant residual blood volume in the clamped tubes may comprise a stagnant area for blood, as the blood flows through the arterial tube and the venous tube. Such stagnant areas for blood are likely to clot, which of course is undesirable. Such a substantially complete seal of a length of the transverse blood tubing as defined herein, or other blood tubing, is defined to comprise enough sealing closure of the tube to eliminate stagnant areas that can clot in normal operation.
Similarly, the wall-to-wall spacing between the sections of the arterial and venous tubes which are between the spaced, transverse tubes should be proportioned so that those sections of the arterial and venous tubes may be substantially completely sealed by the closure of the one or two hemostat clamps, or the like, to similarly provide a minimal residual blood volume, and essentially no clotting while at the same time not significantly collapsing the transverse tubes or other portions of the arterial and venous tubes.
Thus, a variable flow path maybe provided through the section which comprises the transverse tubes and adjacent arterial and venous tubes. The hemostat may close off the two transverse tubes in one flow position, causing blood flow to take place first through the arterial tube from the patient toward the blood treatment device, and then for the blood to pass through the venous tube away from the blood treatment device back toward the patient. However, when the hemostat closes off those portions of the arterial and venous tubes which are between the transverse tubes, the flow of the blood path is entirely different. The return blood from the treatment device passes from a first portion of the venous tube into a portion of the former arterial tube and then back to the patient. Flow from the arterial tube portion adjacent the device continues toward the blood treatment device, and draws blood from the former venous tube portion adjacent to the patient through the changed flow path, so that the flow in the arterial and venous tube portions adjacent to the patient is reversed, while the flow in the other arterial and venous tube portions spaced from the patient by the transverse tubes can remain constant, being typically driven by a roller pump.
Specifically, the distance between the spaced, transverse tubes, suitable for blood flows of about a hundred to a thousand ml./min., from wall to wall is preferably about 0.3 to 1.2 cm, while the corresponding spacing between the arterial and venous tubes is similarly about 0.3 to 1.2 cm. Stagnant areas may thus be avoided if the hemostat clamp or other clamp sealing member is of sufficient width to form a substantially complete seal of the entire lumen of each transverse tube in one instance, or the arterial and venous tubes between the spaced, transverse tubes in the other instance, to minimize stagnant areas for blood without significantly collapsing the tubes which are intended to be open. Specifically, the stagnant areas for blood adjacent to the clamp sealing member used should preferably comprise a total volume of no more than about one ml. for normal tubes of about 4-5 mm. inner diameter.
This maybe facilitated when the spaced, transverse tubes join the arterial and venous tubes with overall spacing to define a symmetrical structure having four flow paths extending therefrom, and where the flow paths are also generally of similar shape, to provide generally uniform pressure drop conditions in the respective alternative situations where (1) flow is blocked by clamp sealing in the transverse tubes and (2) flow is blocked by clamp sealing in the arterial and venous tubes between the spaced, transverse tubes. Typically, this symmetrical structure is in the form of a square.
The spaced, tubes form a quadrilateral figure, particularly a square but alternatively a rectangle, parallogram, or rhombus, without crossing tubes.
Preferably, the set portion of this invention has arterial and venous tubes which each have a tube connector on each end, for respective connection with arteriovenous (AV) fistula needle sets and additional tube sets, for the completion of an overall tubular circuit system for the circulating of blood between a patient and an extracorporeal blood treatment device, such as a dialyzer. Preferably, in the case where the set portion of this invention is separate from the remainder of tubing sets that form the complete circuit, the arterial and venous tubes of the set portion each have a length of no more than about 100 cm. The tube connectors on the arterial and venous tubes may comprise luer type connections, which are a thoroughly tested and reliable type of connector, although other connectors may also be used.
Conventionally sized blood flow tubing may be used. Particularly, the inner diameter of the spaced, transverse tubes maybe about 1.5 to 10 mm. and their outer diameter maybe about 1 to 5 mm larger. Typically, pediatric tubes may have inner diameters of 1.5-4 mm; normal tubes may have inner diameters of 4-5 mm; and cardiovascular tubes may have inner diameters of 5-10 mm.
The arterial and venous tubes may have similar inner and outer diameters, especially at the positions extending between the spaced, transverse tubes.
Flow is controlled and reversed by the occlusion of two of the tubes which form a typically square array of tubes provided by the two spaced, transverse tubes and the arterial and venous tube portions to which they connect. For example, if both of the spaced, transverse tubes are closed with one or two hemostats, then blood flow proceeds normally, first through the arterial tube to reach the dialyzer, with the blood then passing through the dialyzer and back to the venous tube, through which it travels, and then is returned to the patient. However, if the arterial and venous tubes are clamped at their positions between the spaced, transverse tubes by one or more hemostats, then the blood flow, driven by a pump in the circuit, continues to pass blood in the normal way through the dialyzer, but the flow of blood in the tubes extending between the patient and the spaced, transverse tubes is reversed because of the change in the flow path.
This provides an extremely easy way, without any rotary valve or the like, to reverse the flow of blood into and out of the patient while maintaining the same blood flow direction through the extracorporeal blood treatment device. The direction of blood flow with respect to the patient can thus be easily controlled to flow in either direction, simply by proper manipulation of a hemostat or similar device.